Make sure we always have the language code in the URL

classes/controller.php

@@ -117,6 +117,11 @@ class AdminController
         }
 
         $base = $this->admin->base;
+
+        if ($base[3] !== '/') {
+            $base = '/' . $this->grav['session']->admin_lang . $base;
+        }
+
         $path = trim(substr($this->redirect, 0, strlen($base)) == $base ? substr($this->redirect, strlen($base)) : $this->redirect, '/');
 
         $this->grav->redirect($base . '/' . preg_replace('|/+|', '/', $path), $this->redirectCode);